The byproducts of waste incineration are bottom ash, which is removed from the bottom of an incinerator, and bag ash. The typical proportion of the two ashes are 1:1 on a weight bases, but may vary depending upon many processing parameters.
A typical formulation for vitrification of these two ashes thus would combine equal quantities of bottom and bag ashes together with sufficient quantities of additives to form a glassy material. The objectives are 1) to use a minimum amount of additives to obtain the largest waste loading, 2) to have maximum volume reduction from waste to ash and to the final glass form, 3) to minimize the processing cost which is related to the vitrifiable volume, and 4) to have a glassy product which would pass the EPA Toxicity Characteristic Leaching Procedure (TCLP) leachability test.
Incinerators for various wastes, including medical waste, control emissions by injecting a calcium component (calcium hydroxide, bicarbonate, etc.) in the off-gas system. The resulting bag ash which includes both flyash and additives such as calcium compounds, is further reacted with the off-gas stream upon calcining 80 to 90% calcium compounds.
Hydrated lime is used to scrub acid gases from incinerator exhaust off gas streams. Hydrochloric acid is the most common form of acidic contaminant found in the off gas streams of hospital waste incinerators, mainly due to the destruction of large quantities of plastics in hospital waste. The byproduct of the scrubbing reaction is calcium chlorides which form a major portion of bag ash residue when removed from incinerator bag house filters.
In a paper published by Morristown Memorial Hospital entitled "State-Of-The-Art, Small-Scale Medical Waste Incinerator Operating Case History", it is indicated that most of the time, ashes, both pcc bottom ashes and bag house ash, are considered hazardous waste since they fail the EPA TCLP leachability test.